U.S. Pat. No. 3,832,499 (Oscar Heil) discloses an electro-acoustic transducer in which a conductor is arranged in a meander pattern on at least one side of a flexible diaphragm. The flexible diaphragm is pleated or corrugated such that when the diaphragm is placed in a magnetic field oriented in a front to rear axis, with electrical current flowing perpendicular to the magnetic field in one direction in a given fold and in an opposite direction in an adjacent fold, the adjacent folds are alternately displaced to the right and to the left along a third axis perpendicular to both the front to rear axis and to the direction of the electrical current. The air spaces between adjacent folds facing one side of the diaphragm are expanded while the air spaces on the other side are contracted, thereby causing acoustic radiation to be propagated along the front to rear axis.
A two-part article in Speaker Builder (March and April 1982) by Kenneth Rauen discloses alternate designs for the diaphragm of a horn loaded "Heil Air Motion Transformer" ("AMT"), based in part on techniques previously published by Neil Davis (Audio Amateur, February 1977)
Another design for a horn loaded AMT is disclosed in U.S. Pat. No. 5,325,439 (Smiley) and was incorporated in a coaxial speaker marketed by Cerwin Vega (applicant's assignee) as model CATA-15.
However, none of the known prior art designs for a pleated diaphragm transducer provide for both substantially uniform acoustical coupling of the entire effective area of the diaphragm and substantially uniform magnetic flux through that same effective area. Furthermore, no previously known prior art design provides sufficient acoustical loading to match the mechanical impedance of the diaphragm and therefore such prior art designs are unable to maximize the efficiency of the transducer. Accordingly, the known prior art pleated diaphragm transducers are not readily adaptable for high power and high sound pressure level applications such as sound systems for concerts and motion picture theaters.